Comprehensive study on probability of controlling Caspian Sea invasive ctenophora (Mnemiopsis leidyi) (Activity 2: Investigation on Mnemiopsis leidyi diet in the Caspian Sea)

Mnemiopsis leidyi is one the species of comb-jelly. It belongs to the Ctenophore phylum and Lobate order. It is a purely marine, free-swimming animal with a transparent jelly-like walnut-shaped body, which was transported from the Black Sea into Caspian possibly at the end of 1990s. This species is food rival of pelagic fish. It has been reported that the ctenophore caused the dramatic decrease of zooplankton and pelagic fish stock in the Black Sea. In this study, sampling on Mnemiopsis leidyi, zooplankton, phytoplankton was conducted from December 2003 to March 2005, from a total of 11 stations located along four transects (Anzali, Khazarabad, Tourkman and Gorgan Bay) by METU net in the Iranian coasts of the Caspian Sea. Clupeonella catch was done by light fishing with fishing vessel in Anzali region. The results showed that the biomass of M.leidyi had some fluctuation in different seasons and its maximum biomass was recorded in summer with a figure of 524.4±156.2 g.m^2 Tourkman region and the minimum biomass was observed in winter with a figure of 5.15±1.81 g.m^2 in Anzali region. Study of stomach of Mnemiopsis showed, that Acartia (belonged of Copepoda with 66 %), lamlibranchia (13 %) has the highest frequency and the lowest were Balanus nauplii, Rotatoria, Tintinnopsis and Podon polyphemoides. The maximum mean abundance of zooplankton was 29368±24318 n.m3 in winter (Anzali region) and the minimum was recorded 4170±5014 n.m3 in summer (Tourkman region). Copepoda was dominant zooplankton in the Iranian coasts of the Caspian Sea. Chrysophyta with 150000000±440000000 n.m3 and Euglenophyta with 260000±521000 n.m3 had the highest and the lowest frequency respectively in the Caspian Sea. The main foods of Clupeonella were Acartia with 80 %. The survey of stomach of Clupeonella showed that the feeding of these species was not good and the highest fullness index was recorded 220.95±314.67. These results showed, the main food item of Ctenophora and Clupeonella were Copepoda (Acartia). It seems, the impact of Mnemiopsis leidyi feeding has been the important factor in declining zooplankton populations, Clupeonella stocks, and also increasing of phytoplankton abundance

Determination of suitable age and size for releasing of Salmo trutta caspius by evaluation of osmotic

This study was carried out to determine the appropriate size of Caspian trout (Salmo trutta caspius Kessler, 1877) juveniles for releasing to South Caspian Sea or possibility of cage culture in Caspian Sea water. 1611 specimens were exposed in 4 weight groups of 5, 10, 15 and 20 g, in 3 salinity trials: Caspian Water (11- 11.5), inshore water (7) and fresh water (control). Each trial was done in 3 replicates. The blood samples and tissue fixations carried out from juveniles of control group (in fresh water) and 3, 6, 12, 24, 72, 168, 240 hours after exposure of fish in different treatments. Plasma osmolal ity, Na^+ and Cl^- concentrations, were measured by osmometer, flame photometer, RA1000 respectively. Plasma cortisol level was determined by using RIA (radio immunochemical assay). Na^+, K^+-ATPase activity in homogenates of gills was estimated by phosphate released from ATP. Histological indicators including chloride cell diameter and nephron morphometric parameters were assessed using classic preparation and optic microscope with digital camera. Results of osmolality and ions measuring concurrently show that all weight groups can live in salinity of 7 and they maintain the osmolality and ion concentrations. In the Caspian water, weight groups excluding 5 g juveniles show same result. Mean plasma osmolality of 20, 15, 10 and 5 gr juveniles in control group (time of 0) were calculated 331.3±8.7, 307.7±6, 334.7±14.6 and 301±8.7 mosml/l. This parameter in the above weight groups after 240 hours exposure in the Caspian Sea water were measured 329±0.53, 321±9, 325.3±6.7 and 346.5±13.6 respectively. The observation of kidney glomeruli in histological sections shows that the diameter of glomeruli in 5, 10, 15 g weight groups in 7 and all groups in Caspian water decreased after 72 h adaptation period (p0.05) for 5g juveniles, whereas within weight groups of 10, 15 and 20 g in Caspian Sea water and groups of 15, 20 g in water of 7 salinity, the increase (p0.05), although in other groups, a significant increase of this parameter was detected during experiments. Na^+ ,K^+ -ATPase activity in juveniles of 5g weight group in 7 salinity and Caspian water was low (3.2 6.1 mol Pi /mg protein/ h). The enzyme activities in all weight groups were higher under the exposure in Caspian Sea water than that in water of 7 salinity. In group of 10 g juveniles at start time (control in freshwater) the activity of Na^+, K^+ -ATPase was significantly higher (p<0.05) than that in 20g group. It is may be related to some metabolic changes and transforming to parr-smolt